v] POLLINATION AND FERTILISATION 73 



deeply enveloped in protective coverings. The usual 

 isolation of the pollen-grain allows of its free transfer, 

 and the varied mechanisms of flowers secure that the 



-fw 



ti i 



Fig. 15. Ovary of Polygonum convolvulus during fertilisation. fw = 

 wall of ovary : fs = stalk-like base of ovary : /M = funiculus : cha = 

 chalaza : rm = nucellus : wi = micropyle : ii = inner, ie = outer 

 integument : e = embryo-sac : ek = central nucleus of embryo-sac : 

 ei = egg-apparatus: an = antipodal cells : g = style: n = stigma: p = 

 pollen-grains : ps = pollen-tubes. ( x 48. ) (After Strasburger. ) 



